MATERIALS for mechanical, heavy, and upholstery springs are discussed in this paper.
The best practice in making mechanical springs is to use material already hardened. Forming springs of hardened materials makes it easy to detect hardening cracks and nonuniform temper, and longer spring life can be expected.
Heavy springs are those made of stock of large section - so large that the spring must be formed while the material is hot. SAE 1085 and 1090 are actually better heavy-spring materials than the popular SAE 1095 because they have greater endurance.
The ideal material for upholstery springs would have high tensile strength and low elastic limit before fabrication. Afterwards, it would develop a high elastic limit from a low-temperature heating. Cold-drawn products come closest to the ideal.